In psychology, trait theory (also called dispositional theory) is an approach to the study of human personality. Trait theorists are primarily interested in the measurement of traits, which can be defined as habitual patterns of behavior, thought, and emotion.[1] According to this perspective, traits are relatively stable over time, differ across individuals (e.g. some people are outgoing whereas others are shy), and influence behavior. Traits are in contrast to states which are more transitory dispositions.

In some theories and systems, traits are something a person either has or does not have, but in many others traits are dimensions such as extraversion vs. introversion, with each person rating somewhere along this spectrum.

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Gordon Allport was an early pioneer in the study of traits, which he also referred to as dispositions. In his approach, "cardinal" traits are those that dominate and shape a person's behavior; their ruling passions/obsessions, such as a need for money, fame etc. By contrast, "central" traits such as honesty are characteristics found in some degree in every person - and finally "secondary" traits are those seen only in certain circumstances (such as particular likes or dislikes that a very close friend may know), which are included to provide a complete picture of human complexity.

A wide variety later theories and scales have been developed, including:

Big Five personality traits, ("the five-factor model"). Many psychologists currently believe that five factors: neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness. are sufficient.[4][5]

Both the EPQ and Big Five approaches extensively use self-report questionnaires. The factors are intended to be orthogonal (uncorrelated),[6] though there are often small positive correlations between factors. The five factor model in particular has been criticized for losing the orthogonal structure between factors.[7][8]Hans Eysenck has argued that fewer factors are superior to a larger number of partly related ones.[9] Although these two approaches are comparable because of the use of factor analysis to construct hierarchical taxonomies, they differ in the organization and number of factors.

Similarities between lower-order factors for psychoticism and the facets of openness, agreeableness, and conscientiousness (from Matthews, Deary & Whiteman, 2003)

There are two higher-order factors that both taxonomies clearly share: extraversion and neuroticism. Both approaches broadly accept that extroversion is associated with sociability and positive affect, whereas neuroticism is associated with emotional instability and negative affect.[10]

Many lower-order factors, or facets, are similar between the two taxonomies. For instance, both approaches contain factors for sociability/gregariousness, for activity levels, and for assertiveness within the higher order factor extraversion. However, there are differences too. First, the three-factor approach contains nine lower-order factors and the five-factor approach has six.[10]

Eysenck's psychoticism factor incorporates some of the polar opposites of the lower order factors of openness, agreeableness and conscientiousness. A high scorer on tough-mindedness in psychoticism would score low on tender-mindedness in agreeableness. Most of the differences between the taxonomies stem from the three factor model's emphasis on fewer high-order factors.

Although both major trait models are descriptive, only the three-factor model offers a detailed causal explanation. Eysenck suggests that different personality traits are caused by the properties of the brain, which themselves are the result of genetic factors.[14] In particular, the three-factor model identifies the reticular system and the limbic system in the brain as key components that mediate cortical arousal and emotional responses respectively. Eysenck advocates that extraverts have low levels of cortical arousal and introverts have high levels, leading extraverts to seek out more stimulation from socializing and being venturesome.[15] Moreover, Eysenck surmised that there would be an optimal level of arousal, after which inhibition would occur and that this would be different for each person.[16]

In a similar vein, the three-factor approach theorizes that neuroticism is mediated by levels of arousal in the limbic system and that individual differences arise because of variable activation thresholds between people. Therefore, highly neurotic people when presented with minor stressors, will exceed this threshold, whereas people low in neuroticism will not exceed normal activation levels, even when presented with large stressors. By contrast, proponents of the five-factor approach assume a role of genetics[5] and environment[17] but offer no explicit causal explanation.

Given this emphasis on biology in the three-factor approach, it would be expected that the third trait, psychoticism, would have a similar explanation. However, the causal properties of this state are not well defined. Eysenck has suggested that psychoticism is related to testosterone levels and is an inverse function of the serotonergic system,[18] but he later revised this, linking it instead to the dopaminergic system.[19]

Composed of two related but separable traits, Openness to Experience and Intellect. Behavioral aspects include having wide interests, and being imaginative and insightful, correlated with activity in the dorsolateral prefrontal cortex. Considered primarily a cognitive trait.[20]

Scrupulous, meticulous, principled behavior guided or conforming to one's own conscience. Associated with the dorsolateral prefrontal cortex. Anorexics are noted to have higher levels of conscientiousness.[21][22][23]

Gregarious, outgoing, sociable, projecting one's personality outward. The opposite of extraversion is introversion. Extraversion has shown to share certain genetic markers with substance abuse. Extraversion is associated with various regions of the prefrontal cortex and the amygdala.[24][25][26]

"Refers to an individual's tendency to become upset or emotional" (Hans Eysenck) "Neuroticism is the major factor of personality pathology" (Eysenck & Eysenck, 1969). Neuroticism has been linked to serotonin transporter (5-HTT) binding sites in the thalamus: as well as activity in the insular cortex.[30][31][32] Neuroticism also predicts the occurrence of more negative life experiences.[17]

A "favorable or unfavorable attitude toward the self" (Rosenberg, 1965). An individual's sense of his or her value or worth, or the extent to which a person values, approves of, appreciates, prizes, or likes him or herself" (Blascovich & Tomaka, 1991).[33][34][35]

A tendency towards shyness, being fearful and uncertain, tendency to worry. Neonatal complications such as preterm birth have been shown to affect harm avoidance. People affected by eating disorders exhibit high levels of harm avoidance.[36] The volume of the left amygdala in girls was correlated to levels of HA, in separate studies HA was correlated with reduced grey matter volume in the orbito-frontal, occipital and parietal regions.[37][38][39][40]

Risk taking, lack of planning, and making up one's mind quickly (Eysenck and Eysenck). A component of disinhibition. Abnormal patterns of impulsivity have been linked to lesions in the right inferior frontal gyrus and in studies done by Antonio Damasio author of Descartes Error, damage to the ventromedial prefrontal cortex has been shown to cause a defect in real-life decision making in individuals with otherwise normal intellect. Those who sustain this type of damage are oblivious to the future consequences of their actions and live in the here and now.[51][52][53][54][55][56]

Psychoticism is a personality pattern typified by aggressiveness and interpersonal hostility, one of four traits in Hans Eysenck's model of personality. High levels of this trait were believed by Eysenck to be linked to increased vulnerability to psychosis such as schizophrenia. He also believed that blood relatives of psychotics would show high levels of this trait, suggesting a genetic basis to the trait.[65][66]

Persistent, often unwelcome, and frequently disturbing ideas, thoughts, images or emotions, rumination, often inducing an anxious state. Obsessionality may result as a dysfunction of the basal ganglia.[67][68][69]

^Spiegel DR., Qureshi N., The successful treatment of disinhibition due to a possible case of non-human immunodeficiency virus neurosyphilis: a proposed pathophysiological explanation of the symptoms and treatment. doi:10.1016/j.genhosppsych.2009.01.002